1. Field of the Invention
The present invention relates to a photomask to be used in a fabrication process of semiconductor integrated circuits such as liquid crystal displays, a fabrication method of the photomasks, and a fabrication method for semiconductor integrated circuits.
2. Description of the Related Art
A projection exposure apparatus exposures circuit patterns such as semiconductor circuit elements printed on a photomask to a wafer. In addition, it is required for the projection exposure apparatus to have functions of a higher resolution and a fine-pattern reprinted.
In general, when a numerical aperture NA is greater and the wavelength of exposing light is shorter, the resolution of the projection exposure apparatus can be increased. Because the depth of focus becomes small during a pattern printing process when the numerical aperture NA of the projection exposure apparatus is increased, it is limited to increase the numerical aperture NA. Further, when the wavelength of exposure light is changed to smaller wavelength, it must be required to greatly change the pattern printing process.
In the prior art, an improved method to improve an image formation of a photomask has been disclosed. In this improved method, a phase shifter to be used for reversing a phase is formed in a part of a photomask where an exposure light is passed, and a phase of the exposure light is controlled in addition to the control of an amplitude of the exposure light.
For example, there are conventional methods about the phase shifter described in following patent documents: JP-A-57/62052, JP-A-58/173744, JP-A-62/67514, JP-A-62/67547, JP-A-63/304257, and JP-A-3/263045.
FIG. 1A to FIG. 1F are diagrams showing a conventional fabrication method of a photomask. In FIG. 1A to FIG. 1F, the reference number 220 designates a transparent substrate such as a transparent glass substrate, 222 denotes a shade film, and 224 indicates a resist film. When the fabrication process for the photomask is completed, shade patterns 111 are formed on the transparent glass substrate 220 at desired intervals shown in FIG. 1F.
FIG. 2A to FIG. 2F are diagrams showing a conventional fabrication method of a photomask of a low reflection type. In FIG. 2A to FIG. 2F, the reference numbers 231 and 232 designates reflection preventing film formed under and on the shade film 222. When the fabrication process for the photomask is completed, the shade patterns 111 are formed at desired intervals on the transparent glass substrate 220 shown in FIG. 2F. In this configuration, the reflection preventing films 231 and 232 are formed under and on each shade pattern 111.
FIG. 3A to FIG. 3D are diagrams showing a conventional fabrication method of a phase shift photomask. In FIG. 3A to FIG. 3D, the reference numbers 226 designates phase shift sections, and 225 denotes a hollow section (or a cavity section).
In the final fabrication process to fabricate a conventional phase shift photomask, as shown in FIG. 3D, the shade patterns 111 are formed adjacent to the hollow section 225 formed on the transparent glass substrate 220. Further, the phase shift section 226 are formed adjacent to each shade pattern 111.
As described above, a complicated topography or shape is formed on the photomask fabricated by the conventional photomask fabrication methods such as the method to form the shade patterns on the photomask at desired intervals shown in FIG. 1A to FIG. 1F and FIG. 2A to FIG. 2F, and the method to form the phase shift pattern on the photomask at desired intervals shown in FIG. 3A to FIG. 3D.
Thus, because each conventional photomask fabricated by the conventional methods has a complicated topography, it happens that the shade film is fallen or separated from the transparent glass substrate by a brush to be used during a washing process to eliminate dusts. In other words, the conventional photomask has a lower durability during the photomask fabrication process. This drawback of the conventional photomask causes to decrease a reliability of the photomask and to decrease the yield and quality of semiconductor integrated circuits manufactured by using the conventional photomask.
Accordingly, an object of the present invention is, with due consideration to the drawbacks of the conventional technique, to provide photomasks, fabrication methods of the photomasks, and a semiconductor fabrication method of semiconductor integrated circuits such as liquid crystal displays. The photomasks of the present invention have a high mechanical durability during a fabrication process to fabricate the photomask, and has characteristics of a high image formation, a high quality, a high printing precision, and a higher yield in the fabrication process.
In accordance with a preferred embodiment of the present invention, a photomask comprises a transparent substrate, a hollow section formed on a surface of said transparent substrate, a shade pattern including a shade section, said shade section made up of a shade film and formed in said hollow section, and reflection preventing sections, each formed according to one of cases: each reflection preventing section formed on said shade section; each reflection preventing section formed under said shade section; and each reflection preventing section formed on and under said shade section.
In accordance with another preferred embodiment of the present invention, a photomask comprises a transparent substrate, a shade pattern formed on said surface of said transparent substrate, and a phase shift pattern selectively formed on said shade pattern and said transparent substrate. In the photomask, a surface of said phase shift pattern is flat.
In the photomask as another preferred embodiment, an end section of said phase shift pattern that is contacted to said transparent substrate has a sloped shape that is gradually thin.
In the photomask as another preferred embodiment, a difference of a step between said phase shift pattern and said transparent substrate at said end section of said phase shift pattern that is contacted to said transparent substrate is gradually small.
In accordance with a preferred embodiment of the present invention, a photomask comprises a transparent substrate, a hollow section formed on a surface of said transparent substrate, a shade pattern made up of a shade film, said shade film formed in said hollow section, and a phase shift pattern, whose surface is flat, selectively formed on said transparent substrate having said shade pattern formed in said hollow section.
In the photomask as another preferred embodiment, a thickness of an end section of said phase shift pattern contacted to said transparent substrate is gradually thin.
In accordance with a preferred embodiment of the present invention, a photomask comprises a transparent substrate, a hollow section formed on a surface of said transparent substrate, a shade pattern made up of a shade film, said shade film formed in said hollow section, and a phase shift pattern formed on said transparent substrate including said shade pattern formed in said hollow section.
In the photomask as another preferred embodiment, an end section of said phase shift pattern that is contacted to said transparent substrate has a sloped shape that is gradually thin.
In the photomask as another preferred embodiment, said phase shift pattern includes one of or a combination of: a phase shift pattern of a Levenson""s type, a phase shift pattern of an auxiliary shifter type; a phase shift pattern of an edge highlighting type; a phase shift pattern of a half tone type; a phase shift pattern of a half tone type with a shade pattern, a phase shift pattern of a shifter shading type with a shade pattern; and a phase shift pattern of an intermediate phase type.
In accordance with a preferred embodiment of the present invention, a photomask fabrication method comprises the steps of forming a resist film on a transparent substrate, forming a desired pattern on said resist film by developing said resist film after said resist film is selectively exposing by using a radiation ray, forming hollow sections in said transparent substrate by selectively etching said transparent substrate by using said resist film as a mask, eliminating said resist film from said transparent substrate, forming a first reflection preventing film in each of said hollow sections, forming a shade film on said first reflection preventing film formed in each of said hollow sections, forming a shade pattern by performing a chemical and mechanical polishing for said shade film, and forming a second reflection preventing film on said shade pattern. In the photomask fabrication method, said processes for forming said first reflection preventing process and said second reflection preventing process are performed selectively.
In accordance with a preferred embodiment of the present invention, a photomask fabrication method comprises the steps of forming a shade pattern on a transparent substrate, coating a phase shift film on both said transparent substrate and said shade pattern, forming a phase shift pattern by selectively etching said phase shift film by using a radiation ray, and performing a chemical and mechanical polishing for a surface of said phase shift pattern in order to form said phase shift pattern having a desired thickness.
In the photomask fabrication method as another preferred embodiment, after the step of forming said phase shift pattern, further comprises the steps of selectively etching said phase shift pattern by using said radiation ray, and performing said chemical and mechanical polishing for said surface of said phase shift pattern that has been etched in order to form said phase shift pattern having a desired thickness and a flat surface.
In the photomask fabrication method as another preferred embodiment, after the step of forming said shade pattern on said transparent substrate, further comprises the steps of forming a resist film on said shade pattern, forming a resist pattern by selectively etching said resist film by using said radiation ray, selectively etching said transparent substrate by using said resist pattern as a mask, eliminating said resist pattern from said transparent substrate, and performing said chemical and mechanical polishing for said surface of said phase shift pattern.
In accordance with a preferred embodiment of the present invention, a photomask fabrication method comprises the steps of forming a resist film on a transparent substrate, forming a desired pattern on said resist film by developing said resist film after said resist film is selectively exposed by using a radiation ray, forming hollow sections in said transparent substrate by selectively etching said transparent substrate by using said resist film as a mask, eliminating said resist film from said transparent substrate, forming a shade film in each of said hollow sections, performing a chemical and mechanical polishing for said shade film in order to form a shade pattern, forming a phase shift film on said transparent substrate, and forming a phase shift pattern by selectively etching said phase shift film by using said radiation ray.
In the photomask fabrication method as another preferred embodiment, after the step of forming said phase shift pattern by selectively etching said phase shift film by using said radiation ray, further comprises the step of performing said chemical and mechanical polishing for said phase shift pattern formed on said transparent substrate.
In accordance with a preferred embodiment of the present invention, a photomask fabrication method comprising the steps of forming a resist film on a transparent substrate, forming a desired pattern on said resist film by developing said resist film after said resist film is selectively exposed by using a radiation ray, forming hollow sections in said transparent substrate by selectively etching said transparent substrate by using said resist film as a mask, eliminating said resist film from said transparent substrate, forming a shade film in each of said hollow sections, performing a chemical and mechanical polishing for said shade film in order to form a shade pattern, forming a resist film on said transparent substrate in which said shade pattern has been formed, selectively etching said resist film by using said radiation ray, and selectively etching said transparent substrate.
In the photomask fabrication method as another preferred embodiment, after the step of selectively etching said transparent substrate by using said radiation ray, further comprises the step of performing said chemical and mechanical polishing for said transparent substrate.
In the photomask fabrication method as another preferred embodiment, one of an electron beam, a laser beam, and a monochromatic beam is used as said radiation ray.
In accordance with a preferred embodiment of the present invention, a fabrication method of semiconductor integrated circuits such as a liquid crystal display uses said photomask as described above is used.
In accordance with a preferred embodiment of the present invention, a fabrication method of semiconductor integrated circuits such as a liquid crystal display includes said photomask fabrication method according to claim 16 is included.